Spark-plug



R. BREWSTER.

SPARK PLUG. APPLICATION FILED muze, 19m.

Patented De@ 21,1920.

UNITED STATES ROBERT IBREWSTER, OF CHICAGO, ILLINOIS.

SPARK-PLUG.

Specification of Letters Patent.

Patented Dec. 21, 1920.

Application led April 26, 1918. Serial' No. 230,888.

T 0 aZZ whom t may concern:

Be it known that I, ROBERT BREWSTER, a subject of the King of Great Britain, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Spark- Plugs, of which the following is a specification.

My invention relates to improvements in spark plugs.

One of the objects of my invention is to provide a durable, efficient and cheaply constructed spark plug.

I make a spark plug in two pieces, the porcelain or lava core and the screw-threaded shell of, preferably, aluminum, and cast the latter on the formenso that when the structure comes from the die, it is ready for insertion of the central conductor to render it in condition for use. By this means, cost of labor is reduced to the minimum and a very sturdy, stable structure is provided.

In the drawings forming a part hereof Figure 1 shows a central section of the die or mold within which the shell of the plug is cast around the insulating core.

Fig. 2 is a transverse section taken on line 2-2 of Fig. 1.

Fig. 3 is an elevation of the finished plug.

In all the views the same reference char acters are used to indicate similar parts.

The die is made of two pieces, the top part 5 secured to the bottom part 6 by bolts 7, that pass through annular ianges 8 and 9, which are lateral continuations of the respective integral parts 54 and 6.

A removable central stem 10 passes through the lower part into the insulating core 11. The stem supports the core in the part 6 until the part 5 is placed in position thereon. The parts are then secured together with the cap screws 7 A conduit 12 leads into the Space surrounding the core 11 and between which and the sides of the die, 'the threaded shell 13 is to be cast.

Connected to the conduit is a pipe 14 that may lead to a suitable source through which suitable metal, such as aluminum7 an alloy of aluminum, or the like, may be conducted under pressure to the die within which the shell is to be cast around the core.

I p refer to make the central core 11 with a series of annular grooves and projections 15 and 16, respectively, so as to prepare a tortuous path for any gas or air that might tend to escape between the core and shell and furthermore to render the extraction of the shell substantially impracticable. I prefer that these uneven surfaces shall be sinuous, or weavedike in outline, so aS to preserve a. substantially unbroken surface of the vitriiied coating, thereby preventing inequality of expansion and contraction and reducing liability of fracture during the process of casting.

rlhe shell 13 is provided with an angular part 17, by which it may be unscrewed from the die by application of a wrench, when the part 5 of the die is removed and by which the plug may be screwed into a threaded opening, designed to receive it, in the wall of the cylinder of an internal combustion engine.

The threads 18 are cast upon the shell rendering it in condition to be placed within the opening in the engine cylinder, without further work being necessary to fit it in place.

After the structure comes from the die, a central rod or electrode 19, screw threaded at its upper end, as at 20, is placed in the axial opening of the core 11 in place of the rod 10. A washer 21 and nut 22 is threaded over its end to keep it in place and a terminal clamping nut 23 is threaded over the end 20. A terminal 2A may be secured in the lower edge of the shell 13 to provide one of the electrodes for the spark ireliminarily to casting the shell I heat the die and the porcelain core to a temperature of 500 or 600 degrees Fah. so as to expand them to some extent before they are brought into contact with the hot metal so that the metal will set before the heat of the metal causes further expansion of the die and core and therefore the shell may be taken from the die without waiting for the die to cool.

Having described my invention, what I claim is The method of making spark plugs which consists in providing an insulating ieegve core of porcelain having a series of sinuously curved annular projections about which the vitreous coating is continuous, gradually heating Jche core and die, Within which a shell is to be east, to a temperature of a relatively high degree but below melting point of the metal of Which the shell is izo be east "so prevent crizzlin of the p0rcelain surface and pouring tie metal into said die under pressure. 10

ln testimony whereof l hereunto set my hand.

ROBERT BREWSTER. 

